If you want to replace the complete stair assembly for lots of $$ (I assume), there is the GlowGuide stairs along with their Add-A-Step by Torklift.
GlowGuide stairsThere is also the Quadra Step 4 stair setup.
Quadra Step Don't know about the rise measurements and if the overall height is no better than what you have already. Not as expensive as I would have thought. Available at Tweetys for $217 before shipping cost.
TweetysWe have 3 steps on our TT and have wrap around tread covers. When the steps are folded out, the bottom one is often pretty close to the ground and twice in the past season, the underside of the cover has been destroyed by rubbing on the gravel in a campsite from when we walk in and out. I'd gladly have our last step higher off the ground...